Hand-held non-imaging scintillation detectors are used for a number of applications in industry and medicine. These range from contamination monitoring, used to detect radioactive contamination on surfaces or personnel, to use on humans during operations to guide surgeons to areas of high radiopharmaceutical uptake. The high uptake may indicate tumour activity, as in radiolabelled monoclonal antibody work, or a particular organ (eg. parathyroid or lymph node). These ‘intraoperative gamma probes’ have increased in use over the last few years due to the development of a surgical staging technique known as ‘sentinel node biopsy’. This is a method of guiding a surgeon to a lymph node, or nodes, which drains a tumour. Tumours may spread through the lymphatic system and, since lymph nodes may filter out tumour cells travelling in lymph fluid, the first node on the draining lymphatic system is ‘sentinel’—standing on guard against tumour spread.
If the surgeon can remove the sentinel nodes, then the pathologist can closely examine these, and if free from tumour then it is postulated that this shows that tumour has not spread. The patient treatment is therefore planned based upon this staging knowledge, and this technique has been applied most widely for breast cancer, melanoma, and increasingly in other areas (e.g. colorectal).
A number of such intraoperative gamma probes are known, which produce data relating to local gamma radiation flux. These data are often presented in the form of an audible tone or the display of a numerical value. Furthermore, the data generated is highly dependent on the orientation of the hand-held probe in relation to the surface of a patient, leading to inadequate accuracy of localisation of a radiation source. The problem is compounded by the often-encountered low radiation flux, and high background radiation from sources such as the injection site. Also, the presence of several discrete sources in close proximity to each other further reduces the utility of such non-imaging radiation probes.